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View thumbnail for .wmf/.emf files?

Question

In Windows explorer one can view images in thumbnails. For some reasons however, I need to conveniently view a number of .wmf (Windows Metafile) and .emf(Enhanced Metafile) files with thumbnails. I didn’t find it possible with Windows Explorer.

I have also found that I can rename the file directly from .wmf to .emf. For example, many of the formulaes I authored using MathType are stored in unzipped Word .docx folder as .wmf format and double-clicking them opens the
MathType application; however if I rename the corresponding .wmf to .emf, double-clikcing them will open MsPaint.exe (paint), and the originally editable formales (in MathType) will be shown as vector graphics in MsPaint.exe, and they are
NO LONGER recognized as MathType objects.

Do you know why this simple trick of renaming .wmf→.emf could work? I read from
http://en.wikipedia.org/wiki/Windows_Metafile that .wmf is an early 16-bit format whereas .emf is the 32-bit enhanced metafile format. However, I could not understand why as simple as merely a renaming
could result in the conversion between format. Could you explain why this happens?

As an example, two files are contained in http://wikisend.com/download/614206/Euler_formula.rar. The .wmf is the original MathType content, and the .emf is simply the renamed version
with exactly the same content. Windows will use MathType to open .wmf by file type association, and will use MsPaint.exe to open .emf by file name association. I wondered why this simple renaming could work?